Make sure you include a copy-protect feature that causes the interface to crash, eventually locking the owner out of the game he or she paid for. Then the player will be forced to buy the newer version, which will do the same thing.
Hey -- it worked for the makers of Virtual Skipper
I bought both VS3 and VS5, which used the same base coding and some of the same boats/venues. And like many owners, I was eventually prevented from using the games by a buggy copy-protect subroutine. But otherwise ... some likes and dislikes about the games:
-- Decent physics.
-- Movable camera angles, useful as you approach mark roundings.
-- Lay lines, color-changing wind arrows to indicate proper trim, and auto sail trim: all can be turned off as you get good.
-- Fun range of boats, including ORMA trimarans, offshore displacement hull, Melges 24 (tho w/ a symmetrical chute, not an asym), and ACC (the most boring of the bunch. They must be sailed differently -- eg, the tri doesn't point or tack well, but its VMG rewards hotter angles. Head to deep downwind, you'll get lapped.
-- World-building function, where you can make your own islands and race courses.
-- Boat mass never looks quite right. Wave patterns can make you dizzy.
-- some very slow periods, just like real sailing. Most gamers would find those long reaches insanely dull.
-- Clunky menus.
You can buy remaindered versions of Virtual Skipper for a couple bucks. Might be worth looking at. Yiour ideas re: progressing thru boats sounds fun. Just like RL, we're always looking forward to our NEXT boat.